Optical lithography with chromeless phase-shifted masks

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Abstract
Chromeless phase-shifting is a novel concept that completely avoids the use of chrome for pattern formation in optical lithography. This scheme uses 180 degree(s) phase-shifters on transparent glass to define patterns. The method relies on the destructive interference between phase-shifters and clear areas at the edges of the phase-shifters to define dark or opaque areas on the mask. Gratings sufficiently small (named dark-field gratings) will produce sufficient interference to completely inhibit the transmission of light. The combination of these effects makes it possible to form a wide range of patterns, from line-space patterns to isolated bright or dark areas. The lithography simulators SPLAT and SAMPLE were used to understand the principles behind this new scheme, and to verify various pattern designs. Simulation and experimental results are presented to demonstrate the concept.

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